Generally we think of humans having 5 special senses: sight, hearing, smell, taste and touch. Of these senses, sight and hearing are the most important. The organs associated with these sense are the eyes (sight) and ears (hearing), and the brain. Other structures including the optic nerve, retina, vestibulocochlear nerve and tympanic membrane assist these organs in allowing humans to see images and process sounds into things that are meaningful to us.
The eyes are highly developed photosensitive organs for analyzing the form, intensity, and color of light reflected from objects and providing the sense of sight. The eye contains transparent tissues that refract light to focus the image, a layer of photosensitive cells (retina), and a system of neurons that collect, process, and transmit visual information to the brain. The brain takes these signals, which are action potentials, and turns them into an “image” that humans “see”. The retina contains rods and cones, the photoreceptor neurons that will send the signals along to optic nerve to the brain. Rods are responsible for monochromatic vision in relatively dim light and cones provide color vision and tend to function in better in the presence of light . The light sensitive pigment in rods (Rhodopsin) decomposes in the presence of light and triggers a complex series of reactions that initiate nerve impulses on the optic nerve. The 3 sets of cones (red, blue, green), provide color vision and each set contains a different light-sensitive pigment which is sensitive to a different wave length of light. The color perceived depends on which set or sets of cones are stimulated.
The human ear includes the outer ear; the middle ear which consists of the tympanic membrane and auditory ossicles; and the inner ear containing the cochlea, semicircular canals and the vestibulocochlear nerve. The outer ear is responsible for transferring sound waves from the environment to the middle ear. The middle ear is responsible for amplifying sound waves into strong signals for the hearing receptors to detect. And, the inner ear uses mechanoreceptors to detect stimuli for hearing (in the cochlea) and equilibrium (in semicircular canals), and sends the nerve impulses through the vestibulocochlear nerve to the brain. Sounds waves enter the ear and transferred along the nerve as action potentials for the brain to decipher and turn into meaningful sound.
Since these two senses are so important, we have lots of way to determine if they are functioning properly. Sight and hearing tests are routinely done for school-aged children, and as we get older going to the optometrist or audiologist becomes routine. However, in the classroom, it is not easy to determine how the eye and ear works. We can use an eye chart or tuning forks, but that only tells us so much. Using models connected to a computer interface can actually allow us to see the action potentials generated by the eye and the ear based on what colors there are “seeing” and sounds they are “hearing”.